The present invention relates to a technique of detecting information about each of a plurality of rows of nozzles provided in a print head unit of a printer; for example, to a technique of sensing information about the temperature of a transmission gate (hereinafter called a xe2x80x9cTGxe2x80x9d), which is provided in a head drive circuit mounted in a head unit and constituted of a switching circuit for supplying a drive signal to drive elements provided so as to correspond to nozzles for ejecting ink droplets, and sending the temperature information to a control section of a printer main unit.
A color printer which ejects ink of several colors from a recording head has hitherto found widespread use as an output device of a computer. The color printer is widely used for printing an image processed by a computer in multiple gradations of plural colors.
For instance, an ink jet printer ejects ink droplets from a plurality of nozzles of the print head, by actuating piezoelectric elements, which are provided so as to be associated with the respective nozzles, thereby performs printing operation.
The piezoelectric elements that eject ink droplets from the nozzles are actuated by a drive signal supplied from a driver IC (head drive circuit) provided in the print head. The driver IC (head drive circuit) is configured so as to include a TG constituted of a switching circuit for supplying a drive signal to only piezoelectric elements corresponding to nozzles which are to eject ink.
At the time of printing operation, the TG is repeatedly activated or deactivated in accordance with ink ejection timings. The temperature of the TG (based on primarily a junction temperature Tj of a semiconductor used in the TG) increases in accordance with power consumed by the TG. The power consumed by the TG becomes greater on the basis of the magnitudes of activation/deactivation frequencies of the switch; that is, a print speed. Accordingly, if a print speed is increased, the temperature of the TG tends to increase.
The temperature of the TG cannot be set to a value which is greater than a threshold value of the junction temperature Tj (i.e., an allowable temperature) of the semiconductor device used in the TG. For this reason, a temperature margin of the TG becomes smaller with an increase in print speed.
When ink is ejected from the nozzles, the ink serves as a cooler so that an increase in the temperature of the TG can be suppressed. However, in the event that ink has become depleted during a printing operation, the cooling cannot be performed. For this reason, a rise in the temperature of the TG becomes considerable. If the temperature margin of the TG becomes narrow, there will arise a case where the temperature of the TG exceeds the foregoing allowable temperature for reasons of a temperature rise stemming from depletion of ink. In other words, when the-head is filled with ink and ejects ink normally, no temperature error arises. There is a necessity for sensing a rise in the temperature of the TG which would arise at the time of occurrence of an operation failure such as an idle ejecting operation.
To this end, a temperature detection circuit which produces an analog signal corresponding to the temperature of a TG is provided in an IC chip including a TG provided for each row of nozzles in a print head. By way of corresponding signal lines provided in a flexible flat cable (hereinafter called an xe2x80x9cFFCxe2x80x9d), the temperature detection circuits send analog signals corresponding to the thus-detected temperatures of the respective TGs to an A/D converter provided in a controller on a main board within a printer main unit. On the basis of digital outputs from the A/D converter, the temperatures of respective TGs are determined, and the head drive circuit is controlled in accordance with the thus-determined temperatures.
When a plurality of rows of nozzles and, by extension, a plurality of TGs (or IC chips including the TGs) are provided on a head in the manner as mentioned in connection with the case of the foregoing configuration, the FFC must have a plurality of signal lines assigned to the TGs for sensing the temperatures thereof. Consequently, the width of the FFC also increases, thus posing difficulty in the wiring work. Moreover, a signal line for temperature detection is provided for each TG. If the number of TGs is large, a corresponding rise in costs inevitably arises.
It is therefore an object of the present invention to provide a printer which is comparatively inexpensive and can facilitate the wiring work of an FFC, by using only one signal line for detecting temperatures of TGs.
In order to achieve the above object, according to the present invention, there is provided A printing apparatus, comprising:
a print head, including:
rows of plural nozzles, from which ink drops are ejected;
a plurality of driving elements, respectively associated with each nozzle;
a plurality of switching circuits, respectively associated with each row of nozzles, each switching circuit provided with a plurality of switching elements, respectively associated with each driving elements, each switching element supplies a signal to drive an associated driving element; and
a plurality of detectors, each detecting a condition of associated nozzles and outputting a detecting signal in accordance with the detected condition;
a controller, which drives the print head based on the detecting signals;
at least one signal line, which transmits the detecting signals to the controller in a time sequence manner,
wherein the number of the signal line is less than the number of the detectors.
Preferably, each detector detects temperature condition of an associated switching circuit as the detected condition. The detecting signals are transmitted via a single signal line. The controller determines temperature of each switching circuit to drive the print head-based on the determined temperatures.
Here, it is preferable that each detector is provided as a temperature sensor operated in accordance with temperature dependency of a potential difference appearing between a PN junction of a semiconductor.
Further, it is preferable that a temperature of a nozzle situated in a substantially center of each nozzle row is detected representatively as the temperature condition.
Still further, it is preferable that the detecting signals are selectively picked up and transmitted through the single signal line.
In this configuration, preferably, output sides of the respective detectors are commonly connected by an analog switch, through which the detecting signals are selectively picked up.
Alternatively, it is preferable that output sides of the respective detectors are commonly connected by an operational amplifier, through which the detecting signals are selectively picked up, when the operational amplifier is activated.
Further, it is preferable that the detecting signals are picked up every time at least one of when a single page printing is performed and when a cleaning operation for the print head is performed.
Alternatively, it is preferable that the detecting signals are picked up when a high-duty printing is continued for a predetermined time period.
Still further, it is preferable that the selective pickup of the detecting signals is performed based on a signal contained in print data sent to the switching circuits.
Here, it is preferable that information on a least significant digit of the print data is used as the signal to perform the selective pickup of the detecting signals.
Alternatively, it is preferable that the selective pickup of the detecting signals is performed based on a signal contained in program data sent to the switching circuits.
Preferably, the controller is provided with at least one analog/digital converter, each connected with an associated signal line so that the controller detects the detecting signal as a digital signal.
Here, it is preferable that the controller is provided with a print controller of the printing apparatus.
Preferably, each nozzle row is associated with a single color to be printed.
According to the present invention, by means of a simple method any one can be selected from analog signals output from the plurality of temperature sensors. Therefore, only one common signal line to be used for selectively extracting an analog signal output from any one of the temperature sensors is provided in the FFC or the like that connects a recording head to a control section, thus facilitating the wiring work of the FFC.
Accordining to the present invention, there is also provided a print controller of a print head, which includes:
at least two rows of plural nozzles, from which ink drops are ejected;
a plurality of driving elements, respectively associated with each nozzle; and
at least two switching circuits, respectively associated with each row of nozzles, each switching circuit provided with a plurality of switching elements, respectively associated with each driving elements, each switching element supplies a signal to drive an associated driving element,
the print controller comprising:
at least two temperature detectors, each detecting temperature condition of an associated switching circuit and outputting a detecting signal in accordance with the detected temperature condition; and
a controller, which determines temperature of each switching circuit based on the detecting signals transmitted via a single signal line in a time sequence manner to drive the print head based on the determined temperatures.
Accordining to the present invention, there is also provided a temperature detector for a printing apparatus, which includes:
at least two rows of plural nozzles, from which ink drops are ejected;
a plurality of driving elements, respectively associated with each nozzle; and
at least two switching circuits, respectively associated with each row of nozzles, each switching circuit provided with a plurality of switching elements, respectively associated with each driving elements, each switching element supplies a signal to drive an associated driving element; and
a controller, which drives the print head,
the temperature detector comprising:
at least two temperature detectors, each detecting temperature condition of an associated switching circuit and outputting a detecting signal in accordance with the detected temperature condition;
a single signal line for transmitting the detecting signal to the controller in a time sequence manner; and
a temperature determinant provided with the controller, which determines temperature of each switching circuit based on the detecting signals to drive the print head based on the determined temperatures.
Accordining to the present invention, there is also provided a method of driving a print head which includes:
at least two rows of plural nozzles, from which ink drops are ejected;
a plurality of driving elements, respectively associated with each nozzle;
at least two switching circuits, respectively associated with each row of nozzles, each switching circuit provided with a plurality of switching elements, respectively associated with each driving elements, each switching element supplies a signal to drive an associated driving element; and
at least two temperature detectors, each detecting temperature condition of an associated switching circuit and outputting a detecting signal in accordance with the detected temperature condition,
the method comprising the steps of:
selecting one of the detecting signals outputted from the respective temperature detectors;
picking up the selected detecting signal via a single signal line;
determining temperature of an associated switching circuit based on the selected detecting signal; and
driving the print head based on the determined temperature.
Preferably, the selecting step and are repeated so that the detecting signals are picked up via the single signal line in a time sequence manner.